1. Field of the Invention
The invention relates generally to a diesel engine comprising a direct injection injector arranged in the combustion chamber thereof and forming part of a fuel system which comprises a first storage for diesel fuel with a diesel supply conduit and an auxiliary diesel pump, a second storage for LPG with a LPG supply conduit, wherein these supply conduits are connected via a shared conduit to a shared high-pressure pump, wherein the outlet conduit of this high-pressure pump is connected to this injector and wherein a return conduit for fuel is present.
2. Description of the Related Art
Such a diesel engine is described in US 2009/0320786 A1, which is incorporated by reference herein in its entirety. Described herein is the mixing of diesel and LPG in a mixing chamber before it is injected via a common rail system. A return conduit is present here which operates downstream of the high-pressure pump.
The addition of LPG to diesel is interesting for various reasons. Firstly, in certain countries the fuel price of LPG, when calculated according to calorific value, is lower than that of diesel. It has moreover been found that admixing LPG decreases the emission of diesel engines. Particularly the soot emission decreases significantly.
The system described in US 2009/0320786 A1 is found not to be able to function under all conditions. There is a particular risk of transition from liquid LPG to the vapour phase at any location in the conduit system, whereby the dosing of LPG and/or the injection can no longer be accurately regulated in controlled manner. Accurate mixing of LPG and diesel has also been found to be important. This means that it is necessary to ensure under all conditions that the injected fuel always comprises substantially the same ratio of LPG to diesel. After all, if changes occur therein, this has immediate serious effects on both performance and emission.
Known from DE 10 2008 063 278 A1 is a diesel-LPG fuel system with a special mixing tank. The mixing tank is also connected to a return conduit of the injectors. A separate further return conduit connects the mixing tank to the LPG tank.